Linear motor actuators heavily used in various tables of machine tools, moving parts of industrial robots, various transfer apparatuses and the like have functions of giving linear movement to a moving member such as a table and stopping the moving member at a predetermined position. As their driving means, there are used AC linear synchronous motors, AC linear induction motors and the like (hereinafter referred to as linear motors). Such a linear motor is structured to have excitation coils of copper wire wounded on a stator or a mover and energize the excitation coils with exiting current to cause driving power, thereby enabling linear movement.
The power required for the linear motor is determined by the speed and weight of a stage moved by the linear motor. Meanwhile, there are easily available linear motors, which are manufactured under given standards and sometimes do not meet the requirement for desired power. In addition, when the required power is increased, there is a need to design and develop a new linear motor driving device that meets the requirement for increasing power. As the required power is greater, more time and effort are required in development of linear motor driving device and there are many technical problems to be solved.
As to a linear motor device for driving a plurality of linear motors simultaneously, there are following publications. The linear motor driving device disclosed in the publication 1 is a device for synchronously driving two linear motors arranged approximately in parallel, in which device an excitation current required for power generation is generated based on instructions from outside and the generated excitation current is output to each of the linear motors thereby to drive the two linear motor synchronously.
However, this technique is of the linear motor driving device for synchronously driving two linear motors of different specifications, which is different from the present invention relating to the technique of connecting a plurality of linear motors of identical specifications and controlling them as a single linear motor having desired power.
The publication 2 discloses the technique of simultaneously controlling plural linear motors by use of one driver and one linear scale, the linear motors each being for moving an embroidery frame in the x axis direction or y axis direction and the linear motors being externally connected to each other after segmentation of total power. In the publication 2, the plural linear motors are controlled by one driver and one linear scale in such a way that six leads of three-phase winding coils of moving blocks of the linear motors are extended to the outside to connect the plural linear motors to each other externally. Hence, this is different from the present invention which aims to connect a plurality of linear motors of identical specifications and control them as a single linear motor having desired power.
As described above, there is nothing disclosed as to the technique of combining plural linear motors manufactured for general purpose use as standard products to achieve desired power and controlling them to operate like a single linear motor.    [Patent Document 1] Japanese Patent Application Laid-open No. 2003-284388    [Patent Document 2] Japanese Patent Application Laid-open No. 2004-024877